Typical fiber optic connectors require a coupling device which effectively optically couples the fiber optic transmission line with an opto-electronic device (OED). The OED is further electronically coupled to electronic circuits which operate in conjunction with the OED. Often, such electronic circuits, including integrated circuits, are mounted on a printed circuit board or ceramic substrate. These circuit boards/substrates are then densely packed into panels.
To accommodate the use of optical transmission devices in densely packed parallel arrangements of circuit boards, it is commonly required that the fiber optic cable enter the printed circuit board along a path substantially parallel to the board with which it will interface. Complicating this requirement is the fact that commonly-used OEDs have an optical axis that is perpendicular to the substrate. Specifically, a prevalent technology in the optical communications industry is surface emitting and detecting devices. Devices such as vertical cavity surface emitting lasers (VCSELs), surface emitting light emitting diodes as well as most PIN detectors have a photosensitive surface to receive or emit light from or to the top or bottom surface. Because these devices have a vertical optical axis and the fibers are generally parallel to the substrate, an interposer is needed to bend the light between the OEDs and the optical fibers. Some success has been achieved in coupling surface emitting and detecting devices through a 90 degree molded optic coupler as is disclosed in U.S. Pat. Nos. 5,515,468 and 5,708,743 to DeAndrea, et al., the entire disclosures of both of which are hereby incorporated herein by reference. Further examples of such techniques are found in U.S. Pat. Nos. 5,073,003 and 4,904,036 to Clark and Blonder respectively, the disclosures of both of which are hereby incorporated herein by reference.
A more recent interposer, such as those used in active cable assemblies, is shown in FIGS. 1a-f. As shown, the interposer 10 includes a lens body 12 having a ferrule-receiving port 14 for receiving a ferrule such that the end face of the fibers in the ferrule abut an interface surface 16 in the lens body. An array 22 of lenses 24 is disposed along the bottom 26 of the lens body 12. Each lens 24 corresponds to a particular fiber. A reflective surface 20 bends the light traveling between the fibers and the lens 24. Thus, the interposer 10 provides optical paths adapted for optically coupling an OED supported on a substrate with a corresponding fiber supported in the port 14 of the interposer 10. As will be appreciated by those of ordinary skill in the art, such an interposer 10 is suitable for inclusion in various cable assemblies and transceivers, which may be mounted in a variety of host systems including for example, routers, computers, switches, bridges, and I/O cards.
The alignment of the interposer to the substrate, or more particularly, the alignment of the lenses, optical paths and fibers to the OEDs on the substrate, is critical for proper optical coupling between the OEDs and the fibers. Different alignment techniques are used to achieve this alignment. Active alignment techniques are sometimes used to align the interposer relative to a substrate supporting OEDs (such as VCSELs or other light sources) emitting or receiving light substantially perpendicularly to a plane of the substrate. In active alignment, the light sources are activated and emit light. A problem with active alignment is that the process requires special imaging equipment and can be expensive, particularly with respect to light bending optical couplings.
Various passive alignment techniques may also be used. In one passive alignment technique, an image of the light source itself (e.g., a portion of a VCSEL) may be viewed with the human eye through the reflective surface and lenses, thus eliminating the need for special imaging equipment. However, this method requires additional hardware and fixturing to properly view the alignment features, due to tight spacing constraints in the OED assembly. Additionally, this technique is unsafe in that any accidental activation of the light sources will cause damage to the human eye used during the alignment process. That is, since the optical paths for alignment and communication purposes are identical or parallel and/or the alignment feature is the light source itself (e.g., a VCSEL), and thus the eye is in position to be damaged during visual alignment. In yet another passive alignment technique, alignment features are provided on the substrate in the same place as the OEDs. However, in such an arrangement, the alignment structures of the interposer are in a different plane, parallel to and removed from the plane of the OEDs. These alignment features are then viewed through a path external to the reflective surface to eliminate the tight spacing constraints. Although this approach tends to be relatively safe, this method tends to be inaccurate because of the depths of field difference between the two planes exceeds the capability of typical imaging systems. Therefore, in order to achieve alignment, a fixed external reference point must be introduced to which alignment features must be aligned individually. The end result is that the alignment features and alignment structures would be aligned to each other, but the additional step of having to align each to an external reference point introduces additional inaccuracies.
In addition to aligning the lens with the OEDs on the substrate, there is a need to align the fibers with the optical paths in the interposer. One approach is to mount the fibers in a ferrule and then have the ferrule received in the port of the interposer (as described with respect to FIG. 1). Although this approach provides a convenient mechanism and a modular approach for coupling the fibers to the interposer, significant challenges are faced in aligning the ferrule relative to the lens body to enable the port to receive the ferrule, and then holding the ferrule in the port such that the fibers are aligned with the optical paths.
Therefore, Applicants have identified a need for an interposer for coupling an optical fiber to an OED that allows for safe viewing and accurate alignment of any light sources, without the need for special hardware and/or fixturing, using a passive alignment technique. Applicants have also identified a need to align the ferrule with the lens body to enable the port to receive the ferrule and then hold the ferrule in the port precisely such that the fibers are aligned with the optical paths in the lens body reliably and conveniently. The present invention fulfills one or more of these needs among others.